The present invention relates to reduction or elimination of corrosion of hard-friction coated aluminum steam line plug grips.
Steam line plug grips are the essential component used to maintain the purchase of the plug to the nozzle inside diameter and actuate the primary seal O-ring. The design of the grip surface greatly affects the ability of the plug to hold against downstream LLRT test pressure. The grips are made from a high strength aluminum base material and its flat surface has a hard friction coating.
When the grips are removed from service and stored after the outage, the coating tends to delaminate. Subsequent investigation has revealed that the moisture retained in the porosity of the coating after removal from service causes the corrosion of the aluminum base material which results in delamination of the hard friction coating.
One approach to the above problem has been to apply an over coat of penetrant Loctite sealant to the hard friction coating. However, this has not been satisfactory and only a temporary solution at best. The Loctite sealant is an organic material which degrades with time and eventually flakes from the surface.
A need exists to more effectively deal with the porosity of the hard friction coating of steam line plug grips. The present invention seeks to meet that need.
It has now been discovered surprisingly that it is possible to treat the hard friction surface of steam line plug grips with a hard oxide material using CVD in order to fill pores and cracks with CVD material. Surfaces so treated do not readily degrade with use and equipment maintenance is reduced and simplified.
In one aspect, the present invention provides a method of treating a surface of a steam line plug grip comprising subjecting the surface to chemical vapor deposition (CVD) treatment to introduce a hard oxide material into pores and cracks in the surface.
In a further aspect, there is provided a steam line plug grip having at least one CVD treated surface wherein hard oxide material is deposited in pores and cracks of the surface.
Advantages arising from the CVD treatment are that it fills in the pores of the hard friction coating with a hard oxide material, such as for example tantala, titania, silica, or alumina, or other similar oxide which does not readily degrade in use. In addition, the CVD treatment is a conformal surface treatment rather than line of sight, and covers the entire surface thereby allowing for covering the hard friction surface and filling in the pores and cracks with the CVD material. Moreover, the CVD treatment is not a limiting process in that no contaminants come off the surface. There is no delamination of materials from the surface, which is particularly advantageous for components used in a nuclear reactor, such as a BWR or PWR, where contamination of the reactor water is to be avoided. A further important feature is that there is a substantial reduction in corrosion due to the fact the CVD process results not just in coverage of the surface but filling of the pores and cracks, thereby preventing or significantly reducing entry of moisture under the coating.